An escrow is an electromechanical device used to collect or return coins deposited in a pay telephone. The escrow consists of an electrical coil wound around a core implementing an electromechanical solenoid. Several different types of escrow mechanisms exist which require different operating voltages, typically either 48 volts DC or 12 volts DC.
The current state of the art requires either (a) predetermination of escrow coil types or (b) driving all escrow types at a common drive level which suffices for the most power demanding of escrow coil types.
The disadvantage of approach (a) is a lack of flexibility in handling multiple types. In a maintenance environment, multiple escrow types may be used in servicing pay telephones. If a phone is serviced by replacing the escrow unit with a different type, the phone must be reprogrammed in some way to recognize the new escrow type. In a sales environment, when phone electronic kits are sold for retrofitting into existing phone housings, the installer must specify to the phone electronics what type of escrow unit is attached by reprogramming the telephone indicating the escrow type to expect or by use of a mechanical device such as a switch to indicate to the operating program the escrow type to expect which also adds cost.
The disadvantage of approach (b) is a life cycle impairment of low voltage escrow units being driven at high energy levels. This reduces the life of mechanical components by excessive wear caused by hard slapping of mechanical arms.